Temperature probes are used in many applications for measuring the temperature of various objects and environments. U.S. Pat. Nos. 6,592,253 and 7,168,330, in which the Applicant is an inventor, describe prior art embodiments of a temperature probe or combination pressure/temperature transducer, or combination pressure/temperature/flow transducer, respectively.
The fastest temperature probes currently available for critical temperature measurements in extremely corrosive and hostile environments have a thermal time constant of ≧350 ms at best. A temperature probe's thermal time constant determines its response time to temperature measurements and thus, determines its speed.
Speed can be an important consideration when selecting a temperature probe, especially in medical applications where the invasive nature of the measurement, or the particular needs of the patient, may limit the time available to make the measurement. The ability to make high speed temperature measurements also is important in corrosive or hostile environments where prolonged exposure to the media or environment can damage the probe.
The thermal time constant of a temperature probe of any type is the time in seconds, or milliseconds, that it takes the probe to sense and respond to a temperature change of 63.2% of a specific temperature range. Another accepted definition is the length of time that it takes the probe to sense a temperature change from 10% to 90% of a specific temperature range.
A widely accepted temperature range for the measurement and calibration of the time constant of a thin film resistive temperature device (RTD), for example, is the temperature range represented by an agitated ice bath at the lower end and boiling water at the upper end, i.e. 0° C. and 100° C. at sea level, respectively. These two temperatures are often used as a calibration or test temperature range because they are relatively easy to generate and to maintain.
During the manufacture of prior art temperature probes, a production run will occasionally produce a probe with a thermal time constant of ≧250 ms. However, the effective yield in the fabrication of prior art temperature probes is approximately 20%. This means that in a production run of, for example, 10 temperature probes, only 2 probes will perform at a thermal time constant of ≧350 ms.
While the thermal time constants of prior art probes have improved, the improvements have not kept pace with developments in other areas of technology and the associated need to measure temperatures more quickly and in more unstable and hostile environments.
Thus, there is a need in the art for a very high speed temperature probe for making critical temperature measurements, especially in extremely corrosive and hostile environments. Ideally such a high speed temperature probe will have a thermal time constant of at least 200 ms, or better. There also is a need in the art to manufacture such probes with a fabrication yield of 95%, or better, in order to maintain production cost as low as possible.
These and other benefits are realized with the very high speed temperature probe of the present invention.